Principle application of electronic tag

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Radio Frequency Identification (RFID)

RFID is the abbreviation of radio frequency identification, that is, radio frequency identification technology, commonly known as electronic tag.

What is RFID technology?

RFID radio frequency identification is a non-contact automatic identification technology, which can automatically identify the target object and obtain relevant data through radio frequency signals, and can work in various harsh environments without manual intervention. RFID technology can identify high-speed moving objects and multiple tags at the same time, which is quick and convenient to operate.

Ferguson, chief scientist of Accenture Lab, thinks that RFID is a breakthrough technology: "First of all, it can identify a single very specific object, instead of only identifying one type of object like a barcode; Secondly, it uses radio frequency, which can read data through external materials, while barcode must rely on laser to read information; Third, multiple objects can be read at the same time, while barcodes can only be read one by one. In addition, the amount of information stored is also very large. "

What are the basic components of RFID?

The most basic RFID system consists of three parts:

Tag: It is composed of coupling elements and chips, and each tag has a unique electronic code, which is attached to the object to identify the target object;

Reader: a device for reading (sometimes writing) tag information, which can be designed as a handheld or fixed device;

Antenna: It transmits radio frequency signals between the tag and the reader.

A complete system also needs: data transmission and processing system.

What is the basic working principle of RFID technology?

The basic working principle of RFID technology is not complicated: after the tag enters the magnetic field, it receives the RF signal sent by the reader, and uses the energy obtained by the induced current to send out the product information stored in the chip (passive tag, passive tag), or actively sends out a signal with a certain frequency (active tag, active tag or active tag); The reader reads and decodes the information and sends it to the central information system for data processing.

What is RFID middleware?

RFID is one of the top ten strategic technologies suggested by enterprises in 2005. Middleware can be called the center of RFID operation, because it can accelerate the advent of key applications.

The RFID industry has great potential, and its applications cover manufacturing, logistics, medical care, transportation, retail, national defense and so on. According to the report of Gartner Group, RFID is one of the top ten strategic technologies recommended by enterprises in 2005. However, the key to its success lies not only in the price of tags, antenna design, frequency band standardization and equipment certification, but also in the application of Heizai. Middleware can be called the center of RFID operation because it can accelerate the emergence of key applications.

What makes retailers admire RFID so much?

According to the retail analyst of Sanford C. Bernstein, Wal-Mart can save $8.35 billion a year by adopting RFID, most of which is due to the labor cost saved by not having to manually check the bar codes of purchased goods. Although other analysts think that the figure of $8 billion is too optimistic, there is no doubt that RFID can help solve the two biggest problems in the retail industry: commodity shortage and loss (products lost due to theft and supply chain interruption). Now, Wal-Mart loses almost $2 billion a year. If a legitimate enterprise can reach this figure, it can rank 694th in the ranking of the largest enterprises in the United States 1000. Research institutions estimate that this RFID technology can help reduce theft and inventory levels by 25%.

What is the typical application of RFID technology?

Logistics and supply management

Manufacturing and assembly

Air baggage handling

Mail/express parcel handling

Document tracking/library management

Animal identification

Motion timing

Access control/electronic tickets

Road automatic toll collection

Structure and working principle of passive RFID tag

Passive RFID tag itself has no battery, and works by electromagnetic energy emitted by card reader. Because of its simple structure, economy and practicality, it is widely used. Passive RFID tag consists of RFID IC, resonant capacitor C and antenna L. The antenna and capacitor form a resonant loop, which is tuned to the carrier frequency of the card reader to obtain the best performance.

Most manufacturers follow the specifications of the International Telecommunication Union. There are six RFID frequencies, namely 135KHz, 13.56MHz, 43.3-92MHz, 860-930MHz (UHF), 2.45GHz and 5.8GHz. Passive RFID mainly uses the first two frequencies.

RFID tag structure

RFID tag antenna has two antenna forms: (1) wire wound induction antenna; (2) Imprinting or printing the etched spiral antenna on the dielectric substrate. Antenna form is determined by carrier frequency, tag packaging form, performance and assembly cost. For example, when the frequency is less than 400KHz, mH class inductance is needed, and this kind of antenna can only be made of wire wound inductance; When the frequency is 4~30MHz, only a few turns of wire-wound inductor are needed, or an etched antenna on a dielectric substrate is used.

After selecting the antenna, the next step is how to connect the silicon IC to the antenna. There are two basic methods for ic bonding: (1) chip on board (cob); (2) The bare chip is directly attached to the antenna. The former is usually used for wire wound antennas; While the latter is used to etch the antenna. CIB encapsulates the resonant capacitor and RFID IC in the same package, and the antenna is connected to the two external terminals of COB by soldering iron or welding process. Since most cobs are used for ISO cards with ISO standard thickness (0.76), the typical thickness of COBs is about 0.4 mm. Two common COB packaging forms are IOA2(MOA2) adopted by IST and World adopted by HEI Company of the United States.

Direct bonding of bare chips reduces intermediate steps and is widely used in low-cost and large-scale applications. There are also two methods of direct bonding: (1) wire bonding; (2) Flip chip technology. When flip-chip technology is used, a special gold solder ball with a height of about 25 is needed on the chip pad, and then the solder ball is flip-chip on the printed trace of the antenna. The lead wire welding process is simple, the bare chip is directly welded to the antenna with the lead wire, and the welding area is sealed with black epoxy resin. For small batch production, this process has low cost; For mass production, it is best to use flip chip technology.

Basic working principle

The performance of wireless RFID tag is greatly influenced by tag size, modulation form, circuit Q value, device power consumption and modulation depth. Here is a brief introduction to its working principle.

There is a 154-bit memory in RFID IC to store tag data. There is also a modulation gate-controlled transistor (CMOS) with very low on-resistance inside the IC, which works at a certain frequency. When the reader emits electromagnetic waves to make the induced voltage of the tag antenna reach VPP, the device works and sends back data in Manchester format.

Data transmission is accomplished by tuning and detuning the external resonant circuit. The specific process is as follows: when the data is at a logic high level, the gate tube is turned off, and the tuning circuit is tuned to the cut-off frequency of the card reader, which is in a tuning state and the induced voltage reaches the maximum value. In this way, the tuning and detuning generate an amplitude modulation signal on the tag coil, and the card reader detects the voltage waveform envelope, so that the data signal from the tag can be reconstructed.

The switching frequency of the gate control tube is 70KHz, and it takes about 2.2ms to complete all 154 bits of data. After sending all data, the device enters the sleep mode of100 ms. When a tag enters the sleep mode, the card reader can read the data of other tags without any data conflict. Of course, this function is influenced by the following factors: the distance between the tag and the card reader, their direction, the movement of the tag and the spatial distribution of the tag.

Design example

MCRF 355/360 is a 13.56MHz device produced by Microchip company. 355 can be used for COB and direct bonding; 360 has 1 capacitor, and has 100pf inside, only external inductance is needed. The device sends data with a modulation close to 100%, and the modulation depth determines the change of the coil voltage of the tag from "high" to "low", that is, the tuning state and the detuning state are distinguished.

The value of external components is usually optimized to one-third to one-half. For example, if the inductance between antenna A and antenna B is 3 turns, the inductance between antenna B and VSS is 1 turn. When MCRF 355 is made into COB, there are two 68Pf capacitors in series. Capacitor C 1 is connected between antenna a and antenna b, and C2 is connected between antenna b and VSS.

In order to achieve the designed performance, the tag should accurately adjust the carrier frequency of the card reader. However, there will always be deviations in the components used, which will cause changes in the reading distance. The error of inductance can be controlled within 1~2%, so the reading distance is mainly caused by capacitance error. The error of the external capacitor should be within 5%, and the q value should be greater than 100. The internal capacitance of MCRF360R is made of silicon oxide, and the error on the same silicon wafer is less than 5%, while the error in different batches is about 10%.

The memory data of MCRF355/360 can be programmed by the manufacturer before leaving the factory, or it can be programmed by the contact programmer on site.

RFID operating frequency guide and typical applications (1)

RFID products in different frequency bands have different characteristics. In this paper, the characteristics and main applications of passive sensors in products with different working frequencies are introduced in detail.

At present, the working frequency of RFID products is defined as different products that meet different standards in the frequency range of low frequency, high frequency and very high frequency, and RFID products in different frequency bands will have different characteristics. There are passive and active sensors. The characteristics and main applications of passive sensors under different working frequencies are introduced in detail below.

First, low frequency (from 125KHz to 134KHz).

In fact, RFID technology was first widely used and popularized at low frequency. This frequency mainly works by inductive coupling, that is, there is transformer coupling between the reader coil and the inductive coil. The voltage induced by the alternating field of the reader in the inductive antenna is rectified and can be used as the power supply voltage. The magnetic field area can be well defined, but the field strength drops too fast.

Features:

1. Generally, the operating frequency range of inductors operating at low frequency is 120KHz to 134kHz, the operating frequency of Ti is 134.2KHz, and the wavelength of this band is about 2500m.

2. Except for the influence of metal materials, generally low frequency can pass through any material without reducing its reading distance.

3. There is no special license restriction for readers working at low frequency in the world.

4. Low-frequency products have different packaging forms. A good packaging form is too expensive, but it has a service life of more than 10 years.

5. Although the magnetic field area of this frequency drops rapidly, it can produce a relatively uniform reading and writing area.

6. Compared with RFID products in other frequency bands, the data transmission rate in this frequency band is relatively slow.

7. The price of sensors is more expensive than other frequency bands.

Main applications:

1. Animal husbandry management system

2. The application of automobile anti-theft and keyless door opening system.

3. Application of Marathon Running System

4. Automatic parking charge and vehicle management system

5. Application of automatic refueling system

6. The application of hotel door lock system

7. Access control and safety management system

Meet international standards:

A) application of iso11784 RFID in animal husbandry-coding structure

B) application of iso11785 RFID in animal husbandry-technical theory

C) application of iso14223-1RFID in animal husbandry-air interface

D) application of iso14223-2 RFID in animal husbandry-protocol definition

E) ISO 18000-2 defines the physical layer, anti-collision and low-frequency communication protocols.

F) DIN 30745 is mainly the European standard for waste management application definition.

Second, high frequency (working frequency is 13.56MHz)

The inductance of this frequency no longer needs coil winding, and the antenna can be made by etching and living body printing. Inductors generally work by load modulation. That is to say, the voltage on the reader antenna is changed by the load resistance on the switching inductor, and the amplitude modulation of the antenna voltage is realized by using the remote inductor. If people control the on-off of the load voltage through data, then these data can be transmitted from the sensor to the reader.

Features:

1. The working frequency is 13.56MHz, and the wavelength of this frequency is about 22m.

2. Except for metal materials, the wavelength of this frequency can pass through most materials, but it often reduces the reading distance. The sensor needs to keep a certain distance from the metal.

This frequency band is recognized all over the world, and there is no special restriction.

4. Sensors are usually in the form of electronic tags.

5. Although the magnetic field area of this frequency drops rapidly, it can produce a relatively uniform reading and writing area.

6. The system has anti-collision characteristics and can read multiple electronic tags at the same time.

7. You can write some data information into the label.

8. Data transmission rate is faster than low frequency, and the price is not very expensive.

Main applications:

1. Application of book management system

2. Management and use of gas cylinders

3. Management and application of clothing production line and logistics system

4. Three-meter prepayment system

5. Management and application of hotel door locks

6. Large conference personnel access system

7. Fixed assets management system

8. Management and application of medical logistics system

9. Management of intelligent shelves

Meet international standards:

A) ISO/IEC 14443 is close to the coupled IC card, and the maximum reading distance is 10cm.

B) ISO/IEC 15693 loosely coupled IC card, maximum reading distance1m.

C) ISO/IEC 18000-3 This standard defines the physical layer, anti-collision algorithm and communication protocol of 13.56MHz system.

D) 13.56MHz ISM band Class 1 definition 13.56MHz conforms to the interface definition of EPC.

Third, very high frequency (working frequency is between 860MHz and 960MHz)

Very high frequency system transmits energy through electric field. The energy of the electric field does not drop rapidly, but the reading area is not well defined. The reading distance of this frequency band is relatively long, and the passive frequency can reach about 10m. It is mainly realized by capacitive coupling.

Features:

1. In this frequency band, the definitions are different all over the world-the frequency defined in Europe and some Asia is 868MHz, the frequency defined in North America is between 902 and 905 MHz, and the recommended frequency band in Japan is between 950 and 956. The wavelength of this frequency band is about 30cm.

2. At present, the power output of this frequency band is uniformly defined (defined as 4W in the United States and 500mW in Europe). Maybe the limit in Europe will rise to 2W EIRP.

3.VHF radio waves cannot pass through many substances, especially suspended particulate substances such as water, dust and fog. Compared with high-frequency electronic tags, electronic tags in this frequency band do not need to be separated from metals.

4. The antenna of electronic tag is usually long and tag-shaped. The antenna has linear polarization and circular polarization design to meet the needs of different applications.

5. This frequency band has a good reading distance, but it is difficult to define the reading area.

6. It has a high data transmission rate and can read a large number of electronic tags in a short time.

Main applications:

Management and application in supply chain

2. Management and application of production line automation

3. Management and application of air parcels

4. Management and application of containers

5. Management and application of railway parcels

6. The application of logistics management system

Meet international standards:

A) ISO/IEC 18000-6 defines the physical layer and communication protocol of VHF; The air interface defines two parts: type A and type B; Supports both readable and writable operations.

B) EPCglobal defines the structure of electronic article coding, VHF air interface and communication protocol. For example: class 0, 1 class, UHF Gen2.

C) Ubiquitous ID Japan organization, which defines UID coding structure and communication management protocol.

In the future, VHF products will be widely used. For example, Wal-Mart, Tesco, U.S. Department of Defense and Metro Supermarket all applied RFID technology in their supply chains.

Four. Active RFID technology (2.45GHz, 5.8G)

Active RFID has the characteristics of low transmitting power, long communication distance, large amount of transmitted data, high reliability and good compatibility. Compared with passive RFID, it has obvious technical advantages. Widely used in expressway toll collection, port freight management and other application fields.

Radio frequency identification system

An automatic identification system consisting of radio frequency tags, readers and computer networks. Usually, readers emit energy in an area to form an electromagnetic field. When the RFID tag passes through this area, it detects the reader's signal and sends the stored data. The reader receives the signal sent by the radio frequency tag, decodes and checks the accuracy of the data, so as to achieve the purpose of identification.